In conventional boots of this kind, one major problem lies in ensuring continuous, unobstructed sliding movement of the heel when the foot is inserted in the sock or when it is removed.
In fact, in the above-mentioned boot the rear portion of the rear opening of the sock is bounded by an edge constituting the top portion of the heel of the sock, and in proximity to which the lower end of the rear liner is located, so that this liner covers the opening, or the edge of the heel, when the rear cover is closed over the front cover. It should be noted, however, that if, in the closed position, the lower end of the rear liner is positioned substantially continuously with the edge of the heel of the sock, this is not the case in the open position, precisely when the foot is inserted. In fact, since the rear liner is moved by the rear cover to which it is attached, an angular separation of the lower end of the rear liner from the edge of the heel is created in the area in which the rear cover is joined to the shell base, forming a gap which breaks the continuity of the assembly. In use, such a gap causes the heel of the user to be stopped against the above-mentioned edge of the rear portion of the sock when the foot is inserted in it. This, in turn, causes edge to become gradually deformed, thus creating a source of discomfort.
To overcome this difficulty, conventional practice calls for positioning a tongue at the rear base of the front liner, and more specifically on the lower portion of the rear opening of the sock. This tongue is glued or stitched and comprises a free end extending upward. It ensures, in fact, that the rear part of the heel will be enclosed, and thus, by covering the above-mentioned opening for insertion of the foot, closes it and promotes tightening of the lateral edges of the opening.
In this case, the rear liner is made in two parts, one pressed on the rear cover and the other, i.e., the tongue, which is positioned to the rear of the front liner. This leads to a special arrangement of the tongue, so that its junction with the part of the rear liner attached to the cover is secured without discontinuity, so as to avoid harmful raised areas.
Moreover and above all, as regards comfort when the boot is put on, it is often necessary to manipulate the tongue manually in order to move it aside when the foot is inserted, i.e., to prevent the foot from pushing the tongue downward.
To overcome these difficulties, the creation of a one-piece sock, i.e., without hinged rear liner, has also been suggested.
In the case of a rear-entry boot, it nevertheless proved necessary to provide for possible pivoting of the rear part of the one-piece sock so as to allow insertion of the foot.
To this end, a sock comprising two lateral folds forming a bellows was devised; this arrangement allows the front and rear parts of the sock to follow the opening and closing movements of the front and rear covers.
However, this technique entails other kinds of disadvantages, including the necessity of adapting a very sophisticated molding procedure and the creation of, other areas of discomfort, this time in the area of the folds.